Lapping machine



March 7, 1961 Filed Nov. 9. 1959 J. N. cARMAN ETAL 2,973,605

LAPPING MACHINE 2 Sheets-Sheet 1 March 7, 1961 J.\N. CARMAN ETAL 2,973,605

. LAPPINGMACHINE Filed Nov. 9, 1959 2 Sheets-Sheet 2 'top bed.

Y lower lapping plate 14 atthe same zrate.

2,973,605. .LAPPING MACHINE Justice N. Carman, Gloucester, and Leonard C. De Mild, Jr., Saugus, Mass., assignors to`Carman Laboratories, Inc., Bedford, Mass., a corporation of Massachusetts Filed Nov. 9, 1959, Ser. No. 851,574

11 Claims. (Cl. 51-118) This invention relates to a machine for lapping grinding thin plates such as semiconductor or piezoelectric crystals, and has forvits objects to provide `apparatus which will lap frangible plates to an extreme thinness while maintaining the opposite faces of the plate optically llat and parallel.

According to the invention a machine for lapping a thin plate comprises a lower lapping wheel, a planetary gear system including a planetary carrier for holding and rotating one of said plates over said lower plate thereby to lap one side of said plate,'rneans .to drive said gear system, means for reciprocating said lower wheel and carrier relative to said gearsystem, an upper `lapping i wheel opposed to the lower wheel for lapping the other 55531168 Patent i side of said plate, and means'guiding-said upper wheel so Ythat it rests on apla'te in saidcarrierandis free jto reciprocate withsaid lowerwheel. y Y

For the purpose of `illustration a typical embodiment of the invention is shown in 'the acconlpanying draw'- ings in which: i

Pig. l is a plan view of -a lappingy machine;

Fig. 2 is asection on line 2`2of'Fig. l.; and

Fig. 3 is an enlarged section on line `3-3 of Fig. l.

As shown in the. figures the machine comprises a housing 1 at the top of which is formed aninte'gral bed` 2. Over the bed 2is acover Shaving alcircular opening 5a. A shaft 3 is rotativelysupported in the bed Zby Vbearings 4 and 6, and is sealedby a stuflingbox 7. Keyed to the shaft 3 is'the sun gear 8 of a-planetary gear system which includes aring-gear 9 with internal/teeth Ylil and planetary gears 11.` The ring gear "111 is rotatively supported on an annular boss 1.2 on the ftop`bedf2 while the planetary carrier gears 'llfloat between Ian upper lapping lplate 13 andl a lower lapping plate 14.

The threads ofthe -ring 18 `engagevscrew threads on a gear wheel 19 having internal bearings 2l which permit Ythe gear wheel 19 to rotate in a'vertically ixedpositionl on a tube 22 'depending from the top bed 2,. The ring 1S is locked against rotation by a pinv 23 anchored in the AV reversible motor-"24 vwhose shaft 26 ris journalled in the top v`bed drives a's'pur gear 27 engaging teeth 2S on the gear wheel 19.- The motor is controlled by a timer which periodicallyv reverses itsy drive, for

ing the gear wheel 31S alternately'clockwise and counteropenings 29 through them for holding a disk shaped crystal or like workpiece C whose opposite faces are to be ground by the upper and lower lapping wheels. As shown in Fig. 3, each planetary gear il must be thinner than the workpiece C in order that the opposed lapping plates 13 and i4 bear on opposite faces of the workpiece C. Thus the planetary gears float in the very narrow space between the lapping plates. It will be understood that the thickness of the workpiece is exaggerated for the purposes of illustration, and that a slurry or lapping fluid is introduced between the lapping plates so that the planetary gears are confined sufficiently to maintain substantial parallelism with the lapping plates.

The upper lapping plate 13 tits slidingly over thesun gear shaft 3 and bears with its own Weight on the upper surface of the workpiece in the planetary carrier gears 11. The upper plate 15 has handles 31 facilitating removal of the plate for access to the planetary gears. Each handle has an opening securing a locking pin 32 loosely set in the cover 5. The locking pins may be moved out of the handles 31 to permit the upper lapping plate to be turned before itis lifted off the shaft 3. It

is desirable to turn the lapping plate prior to lifting in order to break the adhesion between the plate and the workpiece and planetary gears causedy by the lapping fluid.

ln the top of the upper lapping plate is formed an annular trough 33 for holding a supply of lapping uid. Typically the lapping fluid is a slurry of Pella oil mixed with a fine abrasive such asaluminum oxide grits of 300 to 600 meshj The slurry is fed to the lapping plates v throughpassages 34 'between the trough 33 andV the lower face of the upper lapping plate 13. The slurry feeds slowly from the trough which need be replenished infrequently. oil by apaddle 36 keyed to the rotating shaft 3. rhe paddle maintains theproper slurry consistency until it is delivered directly through the passages 33 to the lappingzone on each side of the planetary carrier gears l1 between the `plates i3 and *14. As the slurry is distributed inwardly and outwardly Vfrom the passages 34 it ows into an annular discharge trough 35 and thence to a discharge pipe 35a. The abrasive tends to Vsettle out of suspension in the trough 35 ybut is agitated and swept to the discharge pipe by a wiper 40 carried by the rotating ring gear 9. The wiper conforms to the lower end of the annular trough.'`

The planetary gears andthe workpieces carried by them are moved ,in anorbit' between the lapping plates Vby rotation of the sun gear andring gear9. As shownV v in Fig. l, the sun and ring gears are driven by a motor 37. The motor drives a pulley 38 through a slipping y clutch'hav'ing two plates 39. The clutch pulley Sti Vis clockwise. The gear wheel.19 inturn screws the ring 18 4 up and down thereby .reciprocating rthepins 16`and `ther Thelower `lapping'plateV is lannular yin shape and rep ciprocates in an yannular space between the .sun `gear SiV and `ring gear@ ofthe planetary system'. The several 4` planetary'gears 11 extend acrossthe annularfspacebetween the ring gear Sand `the.internal(teetlrltl`of the connected by a belt 41 to -a pulley V42 which is 'connected to a gear reduction box 43 by a shafted. To the shaft 44 is keyed a heavy flywheel whose inertia reflects, back to the slipping clutcn. On one end of the shaftfidof the gear box 43 is a pulley' connectedV sizes are selectedso that the ring gear and sun gear rotate at somewhat diiferent speeds; For example the ring gear may be drivenV atr45 rpm. .and the sun gear at f 4() rpm. in the same direction. Such rotation of the sun and'ring gears will, impart to ythe planetary gears an-orb'ital speednbetweenAQ'and. 45 -'r.p.m. around the sun Ygear and a rotational,speed;r around eachplanetary gear axis of approximatelyli rpm. whenwnormal speed has `"beenreached:

`Because the workpieces .lapped between'` the plate-13 The abrasiveis kept in suspension in the causes very very slow stopping it is advantageous t con' trol the stopping. For this purpose the flywheel is controlled by a simple friction brake 50 applied by a lever Stia to the periphery of the flywheel. A conventional belt brake is equally as eifective in controlling the stopping of the ywheel.

A further and important advantage of the apparatus so far described is afforded by the vertical reciprocatio-n imparted to the lapping plates and the planetary carrier gears between the plates. It is the object of the present apparatus to grind thin semiconductor crystals down to a thickness between 0.003 and 0.009 inch. As previously suggested the planetary carrier gears 11 must be thinner than the crystals, and therefore must be no thicker and a few thousandths of an inch. Such thin gears, meshing with the sun and ring gears in the presence of an abrasive lapping slurry would quickly wear away the teeth of the gears, and require frequent replacement of them. Since the planetary gears are small and readily accessible for replacement after Iremoval of the upper lapping plate, wearing of the planetary carriers is a minor economic and operational factor. But the sun and ring gears are relatively very large and expensive and require considerable time for replacement. According to this invention wearing of these gears is radically reduced by vertically reciprocating the planetary carriers l1 relative to them. The vertical extent of movement of the upper and lower lapping plates and the planetary carriers previously described is approximately the thickness of the sun and ring gears. That is the thin teeth of the planetary gears are moved upwardly and downwardly along the teeth of the sun and ring gears continuously distributing wear over the vertical extent of the sun and ring gear teeth, preventing the lodging of any large abrasive particles in the mesh of the teeth, and at the same time permitting the upper lapping plate to bear on and lap the upper surface of the workpiece C.

Thus the present disclosure is for the purpose of illustration only and the invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. A machine for lapping a thin plate comprising a lower lapping wheel, a planetary gear system including a planetary carrier for holding and rotating one of said plates over said lower plate thereby to lap one side of said plate, means to drive said gear system, means for reciprocating said lower wheel and carrier relative to said gear system, an upper lapping wheel opposed to the lower wheel for lapping the other side of said plate, and means guiding said upper wheel so that it rests on a plate in said carrier and is free to reciprocate with said lower wheel.

2. A machine for lapping a thin plate comprising a lower lapping wheel for lapping one side of the plate, a planetary gear system including sun and ring gears and a relatively thin planetary gear floating in mesh with said sun and ring gears, means to drive said gear system, said planetary gear including means to hold and rotate a plate on said lower wheel, an upper lapping wheel opposed to said lower wheel for bearing on and lapping the other side of said plate, and means to reciprocate the lower wheel on its axis thereby to reciprocate the plate and upper wheel and to move the planetary gear relative to the sun and ring gears thereby to distribute wearing of the sun and ring gears by the planetary gear.

3. A machine for lapping a thin plate comprising a lower lapping wheel for lapping one side of the plate, a planetary gear system including a planetary carrier gear having means to hold a plate on s aid lowerV wheel, and including a sun and a ring. gear having teeth in engagement with the teeth of the carrier for rotating the carrier and plate around said lower wheel, the teeth of said sun and ring gear being substantially thicker axially than said planetary carrier and being secured against axial movement, means to drive said gear system rotatively, an upper lapping wheel opposed to the lower wheel for bearing on and lapping the other side of the plate, means guiding movement of the upper plate along its axis, said planetary gear being thinner than the plate and floating between said ltwo wheels, and means to reciprocate thc lower wheel on its axis thereby to reciprocate the plate, planetary gear and upper Wheel, the teeth of the planetary' carrier gear moving axially of the teeth of the sun and ring gears so as to distribute wear of sun and ring gear teeth over the thickness of the teeth.

4. A machine for lapping a thin plate comprising a lower lapping wheel, a planetary gear system including a planetary carrier for holding and rotating one of said plates over said lower plate thereby to lap one side of said plate, means to drive said gear system, means for reciprocating said lower wheel and carrier relative to said gear system, an upper lapping wheel opposed to the lower wheel for lapping the other side of said plate, means guiding said upper wheel so that it rests on a plate in said carrier and is free to reciprocate with said lower wheel, means on said upper wheel forming a trough for holding a lapping fluid, and a conduit through the upper wheel for delivering tluid directly from the trough to said plate.

5. A machine for lapping a thin plate comprising a lower lapping wheel, a planetary gear system including a planetary carrier for holding and rotating one of said plates over said lower plate thereby to lap one side of said plate, means to drive vsaid gear' system, means for reciprocating said lower wheel and carrier relative to said gear system, an upper lapping wheel opposed to the lower wheel forlapping the other side of said plate, means guiding said upper Wheel so that it rests on a plate in said carrier and is free to reciprocate with said lower wheel, means on said'upper wheel forming an annular trough substantially coaxial with said lower wheel, and a plurality of conduits through the upper wheel and evenly distributed around the annular trough.

6. A machine for lapping a thin plate comprising a lower lapping wheel, a planetary gear system including a planetary carrier for holding and rotating one of said plates over said lower plate thereby to lap one side of said plate, means to drive said gear system, means for reciprocating said lower Wheel and carrier relative to said gear system, an upper lapping wheel opposed to the lower wheel for lapping the other side of said plate, means guiding said upper wheel so that it rests on a plate in said carrier and is lfree to reciprocate with said lower wheel, means on said upper wheel forming a trough for holding a lapping uid, a conduit through the upper wheel for delivering iluid directly from the trough to said plate, and means connected to said drive means to agitato the fluid in said trough.

7. A machine for lapping a thin plate comprising a.

lower lapping wheel, a planetary gear system including a planetary carrier for holding and rotating one of said plates over said lower plate thereby to lap one side of said plate, means to drive said gear system, means for reciprocating said lower wheel and carrier relative to said gear system, an upper lapping wheel opposed to the lower wheel for lapping the other side of said plate, means guiding said upper Wheel so that it rests on a plate in said carrier and is free to reciprocate with said lower wheel, means on said upper wheel forming an annular trough for holding a suspension of lapping fluid, a conduit through said wheel for delivering uid directly to thc plate, the aforesaid gear system drive means including a rotating shaft extending through said upper wheel coaxially of the trough, and means on said shaft rotating therewith and extending into said trough tokeep said fluid in suspension by agitation. f Y Y 8. A machine for lapping a thin plate comprising a lower lapping wheel, a planetary gear system including a planetary carrier for holding and rotating one of said plates over said lower plate thereby to lap one side of said plate, means to drive said gear system, means for reciprocating said lower wheel and carrier relative to said gear system, an upper lapping wheel opposed to the lower wheel for lapping the other side of said plate, means guiding said upper wheel so that it rests on a plate in said carrier and is free to reciprocate with said lower wheel, said drive means including a motor, a slipping clutch, and an inertial device between the clutch and said gear system whereby the gear system is accelerated slowly.

9. A machine for lapping a thin plate comprising a lower lapping wheel, a planetary gear system including a planetary carrier.- fonholding and rotating one of said plates over saidlower plate thereby to lap one side of said plate, means to drive said gear system, means for reciprocating said lower wheel and carrier relative to said gear system, an upper lapping wheel opposed to the lower wheel for lapping the other side of said plate, means guiding said upper wheel so that it rests on a plate in said carrier and is free to reciprocate with said lower wheel, a housing forming a iluid collection chamber below said lower plate, an outlet from said chamber, and means connected to said chamber for carrying fluid through said chamber to said outlet.

10. A machine for lapping a thin plate comprising a lower lapping wheel for lapping one side of the plate, a planetary gear system including atplanetary carrier gear having means to hold a plate on said lower wheel, and including a sun and a ring gear having teeth in engagement with the teeth of the carrier for rotating the carrier and plate around said lower wheel, means to drive said gear system rotatively, an upper lapping wheel opposed to the lower wheel for bearing on and lapping the other side of the plate, means guiding movement of the upper plate along its axis, means to reciprocate the lower wheel on its axis thereby totreciprocate therplate, planetary gear and upper wheel, means to introduce a lapping l'luid between said wheels, a housing forming a iluid collection chamber below said lower wheel and an outlet from said chamber, and means carried by one of said sun and ring gears for carrying iluid through said chamber to said outlet.

11. A machine for lapping a thin plate comprising a lower lapping wheel for lapping one side of the plate, a planetary gear system including a planetary carrier gear having means to hold a plate on said lower wheel, and including a sun and a ring gear having teeth in engagement with the teeth of the carrier for rotating the carrier and plate around said lower wheel, the teeth of said sun and ring gear being substantially thicker axially than said planetary carrier and being secured against axial movement, means to drive said gear system rotatively including a rotating shaft connected to said sun gear and extending through said upper wheel, an upper lapping wheel opposed to the lower wheel for bearing on and lapping the other side of the plate, said planetary gear being thinner than the plate and oati'ng'between said two wheels, means to reciprocate the lower wheel on its axis thereby to reciprocate the plate, planetary gear and upper wheel, the teeth of the planetary carrier gear moving axially of the teeth of the sun and ring gears so as to distribute wear of sun and ring gear teeth over the thickness of the teeth, means on said upper wheel forming a trough holding a suspension of lapping fluid, conduit means through said upper wheel for delivery of iluid to said plate, and means on said shaft rotating therewith and extending into said trough to keep said fluid in suspension by agitation.

References Cited in the file of this patent UNITED STATES PATENTS Indge May 31, 1955 

